Method for transmitting and receiving data in a wireless communication system

ABSTRACT

A method of transmitting and receiving data in a wireless communication system is disclosed. In the method of transmitting the data in the wireless communication system, a base station transmits downlink data to a first terminal supporting a first system through a first zone of a frame, and transmits downlink data to a second terminal supporting a second system through a second zone located at a location separated from the first zone backwardly by a frame offset on a time axis. The wireless communication system may support a bandwidth of 8.75 MHz, the frame offset is an offset between a start point of a frame for the first system and a start point of a frame for the second system, and the first zone includes 3+6*(frame offset−1) Orthogonal Frequency Division Multiplexing (OFDM) symbols.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method of transmitting and receiving data in awireless communication system.

2. Discussion of the Related Art

Recently, standardization of an IEEE 802.16m system is in progress.However, IEEE 802.16e terminals of the related art have already comeinto wide use at a point of time when the IEEE 802.16m system iscommercially available. Accordingly, the IEEE 802.16m system needs to bestandardized to be compatible with the IEEE 802.16e system. The IEEE802.16m system requires a frame structure capable of supporting an IEEE802.16e terminal.

The frame of the IEEE 802.16m system includes a plurality of subframes.A subframe includes a plurality of subcarriers on a frequency axis andincludes a plurality of OFDM symbols on a time axis. Some of theplurality of subframes included in one frame are used for transmittinguplink data and the rest are used for transmitting downlink data.

In order to support the IEEE 802.16e terminal, the IEEE 802.16m systemuses some downlink subframes for the IEEE 802.16m system and uses therest of the downlink subframes for the IEEE 802.16e system. A zone usedfor the IEEE 802.16e system is called a wireless metropolitan areanetwork orthogonal frequency division multiple access downlink zone(hereinafter, referred to as “WirelessMAN OFDM DL zone”) and a zone usedfor the IEEE 802.16m system is called an Advanced Air Interface downlinkzone (hereinafter, referred to as “Advanced Air Interface DL zone”).

A downlink frame structure with a bandwidth of 8.75 MHz of the IEEE802.16m system according to the related art will be described withreference to FIGS. 1 and 2.

FIG. 1 is a diagram showing a downlink frame structure according to therelated art in the case where a frame offset is 1, and FIG. 2 is adiagram showing a downlink frame structure according to the related artin the case where a frame offset is 2.

The frame offset according to the related art defines an offset betweena start point of a frame for an IEEE 802.16e system and a start point ofa frame for an IEEE 802.16m system in the unit of subframes. However,since the frame for the IEEE 802.16m system includes one or moredownlink subframes, the frame offset is an integer equal to or greaterthan 1 and less than the number of downlink subframes. For example, ifone frame includes five downlink subframes, the frame offset is aninteger equal to or greater than 1 and less than 5.

The subframes for the IEEE 802.16m system may be divided into fourtypes. A type 1 subframe includes six OFDM symbols, a type 2 subframeincludes seven OFDM symbols, a type 3 subframe includes five OFDMsymbols, and a type 4 subframe includes nine OFDM symbols.

As shown in FIGS. 1 and 2, in the frame structure of the related art,the WirelessMAN OFDMA DL zone includes a type 1 subframe. That is, theWirelessMAN OFDMA DL zone includes six OFDM symbols in FIG. 1 and theWirelessMAN OFDMA DL zone includes 12 OFDM symbols in FIG. 2. A preambleis allocated to a first OFDM symbol of the frame for the IEEE 802.16esystem and a FCH and a DL-MAP are allocated to second and third OFDMsymbols.

A subchannelization method of the IEEE 802.16e system includes partialusage of subchannel (hereinafter, referred to as “PUSC”), full usage ofsubchannel (hereinafter, referred to as “FUSC”) and adaptive modulationand coding (hereinafter, referred to as “AMC”). The PUSC includes twoOFDM symbols, the FUSC includes one OFDM symbol, and the AMC includesthree OFDM symbols. The second and third OFDM symbols, to which the FCHand the DL-MAP are allocated, are subchannelized by the PUSC.

Accordingly, referring to FIG. 1, odd OFDM symbols are present in aportion excluding portions, to which the preamble, the FCH and theDL-MAP are allocated, in the WirelessMAN OFDMA DL zone.

However, when the odd OFDM symbols are subchannelized, a FUSC orBand-AMC method should be used. Therefore, in order to report that thesubchannelization method is changed, a control message should betransmitted to a terminal. If subchannelization is performed using thePUSC and subchannelization is then performed using another method,resources can not be consecutively used.

As described above, in the frame structure of the related art, since thecontrol message should be transmitted in order to inform the terminalthat the subchannelization method is changed, overhead is increased. Inaddition, when the subchannelization is changed, resources can not beconsecutively used. Thus, radio resources are wasted.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method oftransmitting and receiving data in a wireless communication system thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method oftransmitting data using a frame structure able to improve efficiency ofa wireless communication system.

Another object of the present invention is to provide a method oftransmitting data, which is capable of reducing overhead and efficientlyutilizing radio resources.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of transmitting data in a wireless communication system includes,at a base station, transmitting downlink data to a first terminalsupporting a first system through a first zone of a frame; andtransmitting downlink data to a second terminal supporting a secondsystem through a second zone, wherein the second zone is located behindthe first zone by a frame offset on a time axis, wherein the wirelesscommunication system supports a bandwidth of 8.75 MHz, the frame offsetis an offset between a start point of a frame for the first system and astart point of a frame for the second system, and the first zoneincludes 3+6*(frame offset−1) Orthogonal Frequency Division Multiplexing(OFDM) symbols.

In another aspect of the present invention, a method of receiving datain a wireless communication system includes, at a terminal, receivingdownlink data through a second zone of a frame, wherein the second zoneis located behind a first zone by a frame offset, wherein the first zoneis used for transmitting downlink data to another terminal supporting asystem different from a system supported by the terminal, wherein thewireless communication system supports a bandwidth of 8.75 MHz, thefirst zone includes 3+6*(frame offset−1) Orthogonal Frequency DivisionMultiplexing (OFDM) symbols, and the frame offset is an offset between astart point of a frame for the first system and a start point of a framefor the second system.

At this time, the wireless communication system may support a type 1subframe including six OFDM symbols and a type 2 subframe includingthree OFDM symbols.

All subframes included in the second zone may be type 1 subframes.

The embodiments of the present invention have the following effects.

First, since a subframe including three OFDM symbols is included in aframe offset, all OFDM symbols can be subchannelized using one methodand thus overhead can be reduced.

Second, since a second zone includes only a type 1 subframe, a physicallayer structure of the related art may be utilized.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram showing a downlink frame structure according to therelated art in the case where a frame offset is 1;

FIG. 2 is a diagram showing a downlink frame structure according to therelated art in the case where a frame offset is 2;

FIG. 3 is a diagram showing a frame structure of a Time DivisionDuplexing (TDD) wireless communication system with a bandwidth of 8.75MHz and a Cyclic Prefix (CP) which is ⅛ of an available symbol time;

FIG. 4 is a diagram showing a frame structure according to a firstembodiment of the present invention in the case where a frame offset is1;

FIG. 5 is a diagram showing a frame structure according to the firstembodiment of the present invention in the case where a frame offset is2;

FIG. 6 is a diagram showing a frame structure according to the firstembodiment of the present invention in the case where a frame offset is3;

FIG. 7 is a diagram showing a downlink frame structure according to asecond embodiment of the present invention in the case where a frameoffset is 1;

FIG. 8 is a diagram showing a downlink frame structure according to thesecond embodiment of the present invention if a type 1 subframe isincluded in a second zone;

FIG. 9 is a diagram showing a downlink frame structure according to athird embodiment of the present invention in the case where a frameoffset is 1; and

FIG. 10 is a diagram showing a downlink frame structure according to thethird embodiment of the present invention in the case where a frameoffset is 2.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The present invention may be implemented in various forms andis not limited to the following embodiments. In order to clearlydescribe the present invention, portions unrelated to the description ofthe present invention are omitted in the drawings. Wherever possible,the same reference numbers will be used throughout the drawings to referto the same or like parts.

In the entire specification, when any portion “includes” any element,unless explicitly described to the contrary, the word “includes” will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements. The terms “-part”, “-or/-er” and“module” indicate a unit for performing at least one function oroperation, which may be implemented by hardware, software or acombination thereof.

First, a Time Division Duplexing (TDD) frame structure in a wirelesscommunication system in the case where a bandwidth is 8.75 MHz, a CyclicPrefix (CP) is ⅛ of an available symbol time and a ratio of downlink touplink subframes is 5:2 will be described with reference to FIG. 3. FIG.3 is a diagram showing a frame structure of a TDD wireless communicationsystem with a bandwidth of 8.75 MHz and a CP which is ⅛ of an availablesymbol time.

As shown in FIG. 3, a superframe includes four frames and each frameincludes seven subframes. The superframe includes a superframe header(SFH).

The subframe includes a plurality of subcarriers on a frequency axis anda plurality of OFDM symbols on a time axis. The subframes may be dividedinto four types according to the number of OFDM symbols included in thesubframe. A type 1 subframe includes six OFDM symbols, a type 2 subframeincludes seven OFDM symbols, a type 3 subframe includes five OFDMsymbols, and a type 4 subframe includes nine OFDM symbols. Referring toFIG. 3, three of six subframes are type 1 subframes and the rest aretype 3 subframes.

Seven subframes included in one frame may be used for uplink or downlinktransmission, and a portion for uplink transmission and a portion fordownlink transmission may be subjected to Frequency Division Duplexing(FDD) or Time Division Duplexing (TDD). FIG. 3 shows the frame structurefor the TDD case. A frame, in which a portion for uplink transmissionand a portion for downlink transmission are subjected to FDD, is calledan FDD frame and a frame, in which a portion for uplink transmission anda portion for downlink transmission are subjected to TDD, is called aTDD frame.

The TDD frame is obtained by dividing a frame into a zone for downlinktransmission and a zone for uplink transmission on a time axis. That is,some of a plurality of subframes included in the frame are used fordownlink transmission and the rest are used for uplink transmission. Thenumber of subframes used for downlink transmission and the number ofsubframes used for uplink transmission are determined according to aratio of downlink to uplink subframes. For example, as shown in FIG. 3,five front subframes of seven subframes included in one frame may beused for downlink transmission and two rear subframes may be used foruplink transmission.

A switching time is present between a downlink subframe and an uplinksubframe.

The present invention relates to a method of transmitting downlink datato a terminal supporting a first system and a terminal supporting asecond system through a frame in which a portion for uplink transmissionand a portion for downlink transmission are subjected to TDD.

FIG. 3 shows a frame structure in the case where a base station of awireless communication system supports one system when a bandwidth is8.75 MHz. The wireless communication system needs to support a newsystem as well as the existing system. Accordingly, in the embodiment ofthe present invention, a frame structure in the case where a wirelesscommunication system supports the new system as well as the existingsystem when the bandwidth is 8.75 MHz is proposed.

Next, a method of transmitting data to a terminal supporting a firstsystem and a terminal supporting a second system at a base station of awireless communication system according to a first embodiment of thepresent invention will be described with reference to FIGS. 4 to 6.

According to the present embodiment of the present invention, the basestation divides a plurality of downlink subframes included in a frameinto a first zone and a second zone, transmits a downlink signal to aterminal supporting a first system through the first zone, and transmitsa downlink signal to a terminal for a second system through the secondzone.

A downlink frame structure according to the first embodiment of thepresent invention will be described with reference to FIGS. 4 to 6.

FIG. 4 is a diagram showing a frame structure according to the firstembodiment of the present invention in the case where a frame offset is1, FIG. 5 is a diagram showing a frame structure according to the firstembodiment of the present invention in the case where a frame offset is2, and FIG. 6 is a diagram showing a frame structure according to thefirst embodiment of the present invention in the case where a frameoffset is 3.

The frame offset is an offset between a start point of a frame for thefirst system and a start point of a frame for the second system.

In FIGS. 4 and 5, a horizontal axis denotes time, “p” denotes a preambleof the first system, and “PUSC” denotes a symbol subchannelized by PUSC.The first zone is a zone for communicating with a terminal supportingthe first system and the second zone is a zone for communicating with aterminal for the second system. The frame for the first system startsfrom a first OFDM symbol of the first zone and the frame for the secondsystem starts from a first OFDM symbol of the second zone.

Although FIGS. 4 to 6 show the downlink frame when the ratio of thedownlink to uplink subframes is 5:2, the present invention is notlimited thereto.

As shown in FIGS. 4 to 6, if the ratio of the downlink to uplinksubframes is 5:2, the downlink subframe includes 27 OFDM symbols.

The downlink subframe according to the first embodiment of the presentinvention includes a mini-subframe including three OFDM symbols, fortime alignment with an IEEE 802.16e system. The use of a subframeincluding three OFDM symbols as a first subframe of a downlink framemaintains Transmission Time Interval (TTI) transmission of the unit oftype 1 subframes of the IEEE 802.16m system by using front subframes ofthe downlink frame for the IEEE 802.16e system and using subframesincluding six rear OFDM symbols for the IEEE 802.16m system, if aterminal operating in an IEEE 802.16e system mode and a terminaloperating in an IEEE 802.16m system mode are mixed.

The first zone includes 3+6*(frame offset−1) OFDM symbols. That is, thefirst zone includes three OFDM symbols in FIG. 4, the second zoneincludes nine OFDM symbols in FIG. 5, and the second zone includes 15OFDM symbols in FIG. 6.

The first zone includes a mini-subframe at a foremost portion. If theframe offset is 1, as shown in FIG. 4, the first zone includes one type3 subframe. If the frame offset is 2, as shown in FIG. 5, the first zoneincludes one type 3 subframe and one type 1 subframe. Whenever the frameoffset is increased one by one, the number of type 1 subframes includedin the first zone is increased one by one. That is, the frame offsetincludes the mini-subframe and may further include the type 1 subframe.

All the subframes included in the second zone are type 1 subframes.

Next, a method of transmitting data to a terminal supporting a firstsystem and a terminal supporting a second system at a base station of awireless communication system according to a second embodiment of thepresent invention will be described with reference to FIG. 7. FIG. 7 isa diagram showing a frame structure according to the second embodimentof the present invention in the case where a frame offset is 1.

As shown in FIG. 7, a downlink frame includes 27 OFDM symbols. Thedownlink frame according to the second embodiment of the presentinvention includes three type 2 subframes and one type 1 subframe.

All the subframes included in the second zone are type 2 subframes andthe first zone includes 6+7*(frame offset−1) OFDM symbols.

Since a superframe header of the IEEE 802.16m system is composed of atype 1 subframe, it is preferable that the second zone include at leastone type 1 subframe. Accordingly, as shown in FIG. 8, a downlink framemay be configured such that the type 1 subframe is included in thesecond zone. FIG. 8 is a diagram showing a downlink frame structureaccording to the second embodiment of the present invention if a type 1subframe is included in a second zone.

Referring to FIG. 8, the downlink frame according to the secondembodiment of the present invention includes three type 2 subframes andone type 1 subframe, and the first zone includes 7*(frame offset) OFDMsymbols.

Next, a method of transmitting data to a terminal supporting a firstsystem and a terminal supporting a second system at a base station of awireless communication system according to a third embodiment of thepresent invention will be described with reference to FIGS. 9 and 10.FIG. 9 is a diagram showing a downlink frame structure according to thethird embodiment of the present invention in the case where a frameoffset is 1, and FIG. 10 is a diagram showing a downlink frame structureaccording to the third embodiment of the present invention in the casewhere a frame offset is 2.

As shown in FIGS. 9 and 10, the downlink frame according to the thirdembodiment of the present invention includes 27 OFDM symbols and thedownlink frame includes three type 3 subframes and two type 1 subframes.

Both type 1 subframes may be included in the second zone as shown inFIG. 9 or one type 1 subframe may be included in the first zone and theother type 1 subframe may be included in the second zone as shown inFIG. 10.

The first zone includes 5*(frame offset) OFDM symbols in FIG. 9 and thefirst zone includes 6+5*(frame offset−1) OFDM symbols in FIG. 10.

The embodiments of the present invention can be implemented by a varietyof means, for example, hardware, firmware, software, or a combinationthereof. In the case of implementing the present invention by hardware,the method of transmitting and receiving the data according to theembodiment of the present invention can be implemented with applicationspecific integrated circuits (ASICs), Digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), a processor, acontroller, a microcontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

It is obvious to those skilled in the art that the above embodiments maybe constructed by combining claims having no explicitly statedrelationship or new claims may also be added by amendment after patentapplication.

1. A method of transmitting data at a base station of a wireless communication system, the method comprising: transmitting downlink data to a first terminal supporting a first system through a first zone of a frame; and transmitting downlink data to a second terminal supporting a second system through a second zone, wherein a starting point of the second zone is separated from a starting point of the first zone by a frame offset on a time axis, wherein the wireless communication system supports a bandwidth of 8.75 MHz, the frame offset is an offset between a start point of a frame for the first system and a start point of a frame for the second system, and the first zone includes 3+6*(frame offset−1) Orthogonal Frequency Division Multiplexing (OFDM) symbols.
 2. The method according to claim 1, wherein the wireless communication system supports a type 1 subframe including six OFDM symbols and a type 2 subframe including seven OFDM symbols.
 3. The method according to claim 2, wherein all subframes included in the second zone are type 1 subframes.
 4. A method of receiving data at a terminal of a wireless communication system, the method comprising: receiving downlink data through a second zone of a frame, wherein a starting point of the second zone is separated from a starting point of a first zone by a frame offset, wherein the first zone is used for transmitting downlink data to another terminal supporting a second system different from a first system supported by the terminal, wherein the wireless communication system supports a bandwidth of 8.75 MHz, the first zone includes 3+6*(frame offset−1) Orthogonal Frequency Division Multiplexing (OFDM) symbols, and the frame offset is an offset between a start point of a frame for the first system and a start point of a frame for the second system.
 5. The method according to claim 4, wherein the wireless communication system supports a type 1 subframe including six OFDM symbols and a type 2 subframe including seven OFDM symbols.
 6. The method according to claim 5, wherein all subframes included in the second zone are type 1 subframes. 